Device for generating electrical energy from a vibrating tool

ABSTRACT

A device for generating electrical energy from the vibrations generated by a well bore drill tool during the operation of the tool when drilling oil wells, the device comprising an array of piezoelectric elements mounted in the tool and connected to a vibrating part of the tool for converting vibrations of the tool into electrical energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a new device for obtaining energy,preferably electrical energy, from the vibrations generated by a system,machine, mechanism or tool.

While in this specification the invention will be described in relationto a well bore drilling tool, it should be clear that the invention isnot restricted to this field of application. Thus, the word tool intendto mean any tool, machine, mechanism and device that vibrates inoperation or having at least a part thereof capable of generatingvibrations during operation. Vibrations should be understood as pressurevariations either in solid, hydraulic and/or gaseous means.

The inventive device is preferably for use in tools for drilling wellbores either wells producing gas, water, petroleum, etc. and the energygenerated by the device is available to be directed or undirected fed toelectrical, electronic and/or electromechanical equipment, preferablyequipment employed in activities related to the well.

2. Description of the Prior Art

While it is know to convert mechanical energy into electricity by usingpiezoelectric means, this means have been well used in domestic devicesfor generating electrical arcs for use in several applications and theindustry has used piezoelectric devices for obtaining energy byproducing controlled mechanical impacts.

It is known in the field of the oil, petroleum, industry that the wellbores are drilled by using drilling tools and a lot of information isnecessary before operating the tools. Such information may includeparameters like drilling depths, pressure to which the tools will besubject, temperature in the drilling medium, humidity into the wellbore, chemical components and percentage contents thereof in the medium,etc.

Generally, the tool systems for drilling oil well bores comprise aplurality of tubular members having their ends threaded to permit theconnection to each other, these members are named drill pipes and thesame are coupled to each other as the drilling is progressing and depthis increasing. The assembly of several drill pipes connected into thewell bore is named drill string. With the purpose of adding weight tothe string the bottom length of the string is comprised of tubularmembers having thicker walls, and therefore more weight, named drillcollars. Finally a bit is located at the end to drill the bore throughthe several soil, sand, rock layers. This arrangement of components,comprising the bottom length of the string and including the bit isnamed the Bottom Hole Assembly. During the drilling operation a surfaceequipment causes the drill string and the bit connected thereto torotate. Simultaneously, a drill mud is injected to flow along the boreto prevent the bore from collapsing and to bring the drilled material,removed by the bit, up to the surface.

As it is known in the art, some devices have been developed to feed theelectronic equipment that are housed into the bottom assembly, with suchdevices being designed to record and transmit to the surface equipmentall the data obtained from the well bore during drilling. Since thenumber and kind of recording and transmitting devices have increased andthe amount of information is huge, more and more electrical energy istoday necessary to feed all these measuring devices.

Conventionally, two types of energy sources have been employed toenergize theses devices, batteries, particularly lithium ion batteries,and turbo-hydraulic generators. The lithium batteries have been employedfor many years in the oil field and, while they have been reliable, thecost thereof is very high. In addition, they have a chemical compositionthat makes them very contaminating for the natural environment as wellas they require costly procedures for manipulating, transporting andfinally disposing thereof.

The turbo-hydraulic generators appear as an alternative because of theimportant hydraulic power available while drilling the bore. However,these generators produce alterations in the magnetic field around thedevice thus interfering in the measuring devices such as the magneticguiding devices in the bottom hole assembly. Also, these generators donot tolerate the blocking material employed in the drilling fluid and,because of the high rates of the turbine and the abrasion produced bythe solids in the drill fluid, these generators require frequentservicing.

The technologies employed nowadays in the manufacturing of drill bitshave permitted to obtain bits with remarkably extended life thus thereplacement of worn bits by new ones during the drilling operations arenot so frequent as it was in the past. This is related to thereplacement of batteries or generators because the exhausted batteriesor generators are replaced during the dead periods when the worn bitsare removed and the new ones are installed. Since the number of deadperiods are less than they used to be the batteries and/or generatorslife should be longer in order to accompany the bits replacements. Theimmediate solution for this is to place more batteries, which isexpensive, or to extend the life of the hydraulic generators what is noteasy to do.

It should be very convenient to have an alternative solution to provideelectrical energy for the several equipment, such as bottom holemeasuring and/or recording and/or transmission devices, employed in theoil field.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a devicefor converting mechanical energy from a mechanism into electricalenergy.

It is a further object of the present invention to provide a device forobtaining electrical energy from a tool, mechanism, equipment, machineand the like capable of generating vibrations either in a solid, gaseousor hydraulic medium.

It is another object of the present invention to provide a device forgenerating electrical energy from vibrating tools, the device comprisingpiezoelectric means connected to at least a vibrating part of the toolfor converting vibrations of the tool into electrical energy, with thepiezoelectric means preferably comprising at least one piezoelectricelement subject to variable mechanical pressure and connected to acontrol circuit and to a stress restricting device for protecting thepiezoelectric means, wherein the control circuit preferably comprises atleast one transformer, a rectifying bridge and a tension regulator, andwherein the control circuit includes at least one electrical energyaccumulator.

It is a further object of the present invention to provide a device forgenerating electrical energy from the vibrations generated by a wellbore drill tool during the operation of the tool when drilling oilwells, the device comprising an array of piezoelectric elements mountedin the tool and connected to a vibrating part of the tool for convertingvibrations of the tool into electrical energy that may be used directlyin the tool or may be accumulated for further use.

It is a further object of the present invention to provide a device forgenerating electrical energy from a well bore drilling tool, the devicecomprising at least one assembly of piezoelectric elements housed into amain tubular body of the tool, the tubular body having a first endconnected to a stationary coupling device and a second end connected toa movable coupling device capable of axially moving within the maintubular body for applying varying pressure onto the at least onepiezoelectric elements assembly, the at least one assembly ofpiezoelectric elements being connected to an electronic circuit foradjusting and/or regulating electrical parameters of the electricalenergy.

It is a further object of the present invention to provide a new energygenerating device for use with a drill string, preferably for mountingin the bottom hole assembly and connected to the drill bit, preferablythrough the drill collar or similar connection or coupling.

It is still another object of the present invention to provide a devicefor generating electrical energy from a tool, machine or any mechanismthat vibrates during operation, wherein the device is capable ofconverting these vibrations into electricity to be directly used in themachine, tool or mechanism or for accumulating in correspondingaccumulators, batteries and the like.

It is even another object of the present invention to provide an almoststationary device for generating electricity from the vibrations of atool during operation thereof, the device being independent from thedrill fluid employed in the tool and having extended periods ofoperation with low need of service.

The above and other objects, features and advantages of this inventionwill be better understood when taken in connection with the accompanyingdrawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example in the followingdrawings wherein:

FIG. 1 shows a perspective view of the device according to theinvention;

FIG. 2 shows an exploded perspective view of the device of FIG. 1;

FIG. 3 shows a side elevational view of the device of FIG. 2 with themain tubular body removed from clarity purposes;

FIG. 4 shows a perspective view of the electrical concentring device;

FIG. 5 shows a side elevational view of movement restricting meansforming part of the movable coupling device of the inventive electricalgenerating device;

FIG. 6 shows a perspective view of an assembly of piezoelectric elementsremoved out from the main tubular body and connected to a circuit foradapting, such as adjusting and/or regulating, electrical parameters ofthe electrical energy;

FIG. 7 shows a side elevational view of one array of piezoelectric discs(not shown) housed in an outer casing;

FIG. 8 shows an end view of the left end, female coupling, of the arrayof FIG. 7;

FIG. 9 shows an end view of the right end, male coupling, of the arrayof FIG. 7;

FIG. 10 shows a side elevational view of the array of piezoelectricdiscs of the invention with the outer casing removed for claritypurposes;

FIG. 11 shows an exploded perspective view of the array of piezoelectricdiscs according to the invention;

FIG. 12 shows an enlarged portion of the discs array, the portion beingencircled in FIG. 11;

FIG. 13 shows an exploded perspective view of the stress restrictingdevice for protecting the piezoelectric means against excessive stressand impacts, and

FIG. 14 shows a diagrammatic view of the electric control circuit of theinventive device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring in detail to the invention, the same refers to a deviceindicated by general reference number 1 in FIG. 1, wherein device 1 isan electrical energy generator for use in mechanisms, machines, devices,tools, etc. capable of producing vibrations when operating, with thegenerated electricity being capable of being used by the same machinery,tool and the like for feeding electrical and/or electronic and/orelectromechanical and/or electromagnetic equipment forming part of thetool, preferably a drill string employed in well bores producing oil,gas and/or water.

Device 1 comprises a main tubular body 2 having a first end including,firmly mounted thereto, a stationary coupling device 3, and a secondopposite end including a movable coupling device 4 that has at least apart thereof inside body 2 and that axially moves relative to body 2.Stationary coupling device 3 includes at an inner part thereof a femalethread 5 for coupling a drilling tool, such as a bit, to a drill stringor similar component employed in the drilling of well bores. Inaddition, movable coupling device 4 also includes a male thread 6 withthe same purposes like female thread 5.

Main body 2 includes movement restricting means for restricting theaxial relative movement between main tubular body 2 and movable couplingdevice 4. Movement restricting means comprises a plurality of notches 7,see also FIG. 5, circumferentially extending around body 2 for receivingkeys 8 outwardly radially extending from movable coupling device 4 forlimiting or restricting the axial movement of device 4 within body 2.Each key 8 is attached to device 4 by a screw 9. The details of thesemeans may be clearly appreciated from FIG. 5.

The general inner construction of the inventive device may be describedin connection to FIGS. 2 and 3. The stationary coupling device includesa sealing means, such as a sealing ring 10, for sealing the connectionto an electrical concentring device 11 which will be further described.At the opposite end, movable device 4 includes a force applying collar13 that is fixed to device 4 by screws 12, FIG. 2. Piezoelectric meanscomprising a a plurality of piezoelectric elements, preferably threeassemblies of piezoelectric elements, or piezoelectric assemblies 14,15, 16, are mounted between, and connected to, collar 13 and device 11.A stress restricting device for protecting the piezoelectric systemagainst excessive stress, impacts, pressures, etc. is also provided. Thestress restricting device may comprise one or more restricting elements17, 18, 19, such as springs, high impact resisting rubber pieces,Belleville-type discs springs, hydraulic springs, bumpers, etc.Preferably, the stress restricting device has an adjustable stiffnessfor reaching the mechanical resonance of device 1.

Each assembly of piezoelectric elements is comprised of a plurality ofmodules, preferably three independent modules that are connected to eachother. FIG. 6 shows one of the assemblies, namely assembly 14, thatcomprises an adapting circuit or adapting device 20 and at least onearray 21, 22 of piezoelectric discs. Device 20 and arrays 21, 22 aresubstantially cylindrical and axially coupled to each other by theirends and by means of mechanical and electric couplings. The disc arrayis also connected to restricting or protecting means 17, 18, 19.

Device 20 and arrays 21, 22 are provided at a respective end thereofwith male coupling guides 23, 24, 25 while at opposite ends, the deviceand arrays include corresponding female coupling guides 26, 27, 28. Onlyfemale coupling 28 corresponding to array 22 is shown in FIG. 6.Basically discs arrays 21, 22 are connected in parallel, therefore thecurrents generated by the arrays are summed and the electric tensionsare leveled, with these parameters being fed to adapting device 20 foradjusting and adapting the same.

FIG. 7 shows a side elevational view of one array of piezoelectricdiscs, namely array 22, having a first end 28, defining a femalecoupling, and a second end 25, defining a male coupling. Female end 28,shown by an end view in FIG. 8, comprises a portion of an outercylindrical casing 42 that includes four orifices or coupling bores 36,37, 38, 39, forming a mechanical coupling for receiving pins 32, 33, 34,35, to which reference will be made below, of an adjacent piezoelectricassembly. Female end 28 also includes two notches 43, 44 for receivingelectrical connecting terminals or female contacts 45, 46 forelectrically coupling male terminals. Male end 25, shown in the end viewof FIG. 9, comprises a cylindrical member 41 including four mechanicalcoupling pins 32, 33, 34, 35, axially extending relative to alongitudinal axis of the tubular casing 42, and two electricalconnecting terminals or contacts 30, 31 passing through correspondingorifices 47, 48. A first one 30, 31, of the electrical connectingterminals of first end 28 is electrically connected to a first one 45,46, of the connecting terminals of second end 25 and a second terminal30, 31, of the first end is electrically connected to a second terminal45, 46, of the second end.

The array of piezoelectric discs is shown in FIGS. 10-13 without outercasing 42 in order to have a clear view of the discs. Casing 42 is madeof a non conductive material to enclose the discs into an electricallyisolated environment. Two conductive strips 50, 51 are radially providedagainst an inner surface, not shown, of casing 42, angularly arranged at90° from each other and extending all along the length of the outercasing. Each strip includes a first end defining one of the electricalconnecting terminals 30, 31, and a second end defining one of the femalecontacts 45, 46, formed by a contacting sheet.

A plurality of discs 52 made of piezoelectric material is assembledalong a guiding shaft or stem 53 which is coated or encased into anelectric insulating sheath 54 in order to keep form an insulationbetween the discs and shaft. The piezoelectric material may be selectedfrom ceramics, crystals, composite materials, lead titanate, leadzirconate and any other well know piezoelectric.

Electrically insulating shaft 53 is mounted at a first end thereof incoupling 24 and is electrically insulated by an insulating disc 55. Atthe opposite end, shaft 53 is mounted in a head 56 with an insulatingdisc 57 also arranged between the end the shaft and the head. Head 56 isa cylindrical member having a wall thickness or dimension foraccommodating in the annular surface of insulating disc 57. Theadjustments or fixing of the all package formed by the piezoelectricdiscs over guide shaft 54 is made by an adjusting screw 58 that isthreaded over thread 59 for pre-compressing and compressing the array ofpiezoelectric discs. A spring disc or a well know Belleville disc 60 isarranged between screw 58 and head 56.

As it is shown in FIG. 12, piezoelectric discs are in-parallelconnected. That is, the spaced apart circular sides of two adjacentdiscs 61, 62, namely the left side of disc 61 and the right side of disc62, are electrically connected by a connecting plate 63 that alsoconnects to the right side of a disc (no reference number) adjacent todisc 61 and to the left side of disc 64. In addition, the adjacent orfacing sides of discs 61, 62, namely right side of disc 61 and left sideof disc 62, are connected, by a connecting plate 66, to the adjacent orfacing sides of two adjacent discs 64, 65, namely right side of disc 64and left side of disc 65. Plates 63, 66 are angularly offset betweeneach other, in 90° for example, and are made of any appropriateconductive material, a metal such as copper and the like. This patternis repeated all along assembly 21, 22. Since all plates 66 are inelectrical contact to strip 50 and since plates 63 are in electricalcontact to strip 51, with the strips shown in FIG. 10, the piezoelectricdiscs are connected in-parallel. In this way the several generatedelectrical tensions provide a resulting tension that can be measuredbetween conducting strips 50, 51, between terminals 30, 31 or betweenterminals 45, 46. According to principles of in-parallel connections,the resulting currents will be summed up into a total current.

Making now reference to FIG. 4, concentring device 11 comprises a cavity80 for containing a control circuit, to which reference will be madefurther, and one or more operating equipment, namely measuring,recording, transmission, processing devices generally employed in thedrilling and other oil well activities, which devices are to be fed bythe energy generated by the piezoelectric elements. These devices may beelectrical, electronic or electromechanical devices. Device 11 also hasother cavities, namely cavities 81, 82, 83 for accommodating the flow ofa drill mud employed in the drilling operation. These cavities continuealong the stationary and movable coupling devices, the main tubular bodyand all other components in the energy generating device. Device 11 isnamed concentring device because it is intended to sum up or collect theelectrical energy generated by assemblies 14, 15, 16 and, for thepurpose of describing the circuits in FIG. 14, device 11 is representedby block 99 in this Figure. As it will be seen, control circuit iscomprised of several circuits for modifying and/or adjusting and/orregulating and/or adapting and/or accumulating the generated energy.

Concentring device 11 is connected to adapting circuit or device 20 bytwo wires, not illustrated, passing through orifice 110, with one wireconnecting the positive output (not shown) of assembly 14, throughadapting circuit 20, to concentring device 11. The other wire connectsthe negative output (not shown) of assembly 14, through adapting circuitor device 20, to main body 2 or to any other earth part of device 1. Theconnections of remaining piezoelectric assemblies 15, 16 are carried outin like manner except that the corresponding wires pass through orifices112 and 113 respectively.

FIG. 13 shows a stress restricting device 17, that is identical todevices 18, 19, and that comprises a guide stem 70 and a plurality ofpacks 71 each pack comprised of a plurality of Belleville discs 72axially aligned and mounted over stem 70. Packs 72 are contained byactuator shaft members 73, 74, with member 74 having an actuator shaft75 coupled to member 74 by means of any appropriate seal (not shown) toprovide the system with protection in a hermetic or isolated orwatertight environment. Shaft 70 includes a plurality of orifices 76 atits periphery for permitting inner flowing of a hydraulic fluid, such asoil, for minimizing friction forces between Belleville discs duringoperation of the system. The end of shaft 70, close to member 73 andwithin an orifice in member 73, an equalizing piston 77 is provided forcompensating pressure changes in the hydraulic fluid when the Bellevilediscs are compressed under the forces applied onto actuator shaft 75.

In operation, the vibrations and/or pressure changes in the drill toolwill be converted into energy, more particularly electrical energy, bydevice 1. As it is well known, a quartz crystal provides electricalcharges when the crystal is subject to a pressure deforming the piece ofquartz. This phenomenon is known as piezoelectric effect. The reverseeffect is also well known, when a piece of quartz crystal is subject toan electrical field applied thereto, the crystal reacts by deforming.This is known as reverse-piezoelectric effect. Therefore thesepiezoelectric materials may be employed in converting mechanical energyinto electrical energy.

Both above mentioned effects have been applied in a number of fields.For example, the piezoelectric effect is employed to actuate lighterswherein a lever is employed to apply an impact onto a piezoelectriccrystal thus creating an electrical field that is strong enough to lightthe gas expelled by the lighter. Piezoelectric elements are alsoemployed in alarm clocks. This effect is employed by the presentinvention when operating the drill tool under a huge and constant amountof vibrations and pressure changes. In operation, movable couplingdevice 4 is located towards the bottom of the bore under drilling. Whenthe drill string is still pending without being rested onto the bottomof the hole, stress restricting devices 17, 18, 19 keep device 4 spacedapart from body 2 under the force transmitted by actuator shafts, shaft75 for example, to collar 13. This movement is limited or restricted bykeys 8 and notches 7. In addition, keys 8 prevent the relative rotarymovement between body 2 and coupling device 4.

When beginning the drilling the drill string is moved down and pressureis applied against the drill bit (not shown). Said pressure causes theseparation or gap between main tubular body 2 and movable couplingdevice 4 to decrease and the piezoelectric assemblies 14, 15, 16, and inturn the arrays 21, 22 of piezoelectric discs, are subject tocompression under the effect of the forces transmitted thereto by thestress restricting devices 17, 18, 19 through actuator shaft 75 andcollar 13.

In the drilling, discontinuities, different consistencies and otherirregularities of soil, sand, rocks, etc., cause the bit to move axiallythus producing vibrations along the drill string. Said vibrationsproduce in turn variations in the pressure applied to the array of discs21, 22, which pressures are mechanically restricted or controlled bydevices 17, 18, 19. These restricting or protecting devices are designedto prevent, upon appearance of big accelerations, permanent damages inthe arrays of piezoelectric discs, that is, structural damages,depolarization and the like.

The pressure changes exerted onto the array of discs 21, 22 produces, bypiezoelectric effect, electrical energy. Since the pressure variationsare mostly of low frequency, the total impedance of the array of discsis very high thus producing high voltage or electrical tensions. Thisrequires of the use of adapting circuit or device 20 connected to thepiezoelectric assembly, which device includes an impedance transformerfor adjusting the impedance and voltage values into practical manageablevalues.

Making now more detailed reference to the control circuits of thepresent device, FIG. 14 schematically shows a diagram of the invention.As above disclosed, each piezoelectric assembly 14, 15, 16 is comprisedof arrays 21, 22, now enclosed in blocks as piezoelectric arrays 90, 91,92, and adapting device 20, comprised of impedance transformers 93, 94,95 and complete-wave rectifier bridges, such as diode bridges 96, 97, 98for rectifying the energy generated by each piezoelectric array. Thethree outputs from the rectifiers are fed and summed up into concentringdevice 11, as represented by circular block 99. The electrical energy isthen transferred to a set of capacitors 100 that reduces the wave loopsor curls provided by the rectifiers. Then the energy is sent to acommuting regulator 101 that is commanded by a control module 102.Finally, the output of commuting regulator 101 is connected, as a powersource, to the operating equipment or circuits, such as measuringdevices, transmission equipment, recorders, data storing means, dataprocessing means, sensing devices, etc. which are powered by thegenerated energy. All these devices or operating equipment arepreferably housed in cavity 80 of concentring device 11. Transformers93, 94, 95 and rectifiers 96, 97, 98 of the adapting device 20, as wellas capacitors 100, regulator 101 are at least part of a control circuitthat generally may operate as a circuit for adapting and/or adjustingand/or regulating and/or accumulating the energy generated by theinventive device. Thus, adapting circuit 20, enclosed by phantom linesin FIG. 14, is part of the control circuit, while a further part of thiscontrol circuit is enclosed by the phantom lines at the right side ofFIG. 14 showing that this further part is housed in device 11. Thegenerated energy may be directly fed to the operating equipment,generically known as MWD, or may be stored in an accumulator, such as abattery B.

The maximum output or performance of the inventive device is achieved byadjusting the stiffness of restricting or protecting devices 17, 18, 19in order to reduce the bumping or protection effect thereof. Thus, themaximum movement will produce a maximum force onto the discs arrays,which force will be the result of the product between the mass of thecomponents under vibrations, namely the drill collar and bits foreexample, and the acceleration under which these components are subject.This adjustment would be made without exceeding the maximum pressurethat the arrays of discs may resist. By the above mentioned adjustment amechanical resonance is achieved in the mass of the system thusrequiring less mechanical energy for generating electricity and makingthe system more efficient.

As stated above, while the present energy converter or generator hasbeen disclosed in connection to a drill tool employed in the oilindustry, it is clear that the inventive device may be applied in anymachine or equipment that generates vibrations or pressure variationsfrom which electricity may be obtained. In any event, the device of theinvention, or the array of piezoelectric discs, generates and receivespressure vibrations along an axis according to piezo coefficient g33corresponding to the material of the piezoelectric discs, and/or alongtwo normal axes according to piezo coefficients g33 and g31 for thematerial of the piezoelectric discs. In other words, the pressuresvarying in time are exerted in alignment with the vertical axis of thecolumn or string and according to the properties derived fromcoefficient g₃₃ of the piezoelectric tensor of the piezoelectricmaterial, either with vertical components of the vibration or theresultants of converting into vertical pulses the components of theother two axes of the vibrations. Also, the variable pressures may bealigned to directions or axes normal to the vertical axis of the deviceby using the properties derived from coefficients g₃₁ or g₃₃ of thepiezoelectric tensor of the piezoelectric material.

While preferred embodiments of the present invention have beenillustrated and described, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the scope of the invention as defined in the appendedclaims.

1. Device for generating electrical energy from vibrating tools, thedevice comprising piezoelectric means connected to at least a vibratingpart of the tool for converting vibrations from the tool into electricalenergy.
 2. The device of claim 1, wherein the piezoelectric meanscomprises at least one piezoelectric element subject to variablemechanical pressure, the at least one piezoelectric element beingconnected to a control circuit and to a stress restricting device forprotecting the piezoelectric means.
 3. The device of claim 2, whereinthe control circuit comprises at least one transformer, a rectifier anda tension regulator, for adjusting and/or regulating electricalparameters of the electrical energy.
 4. The device of claim 3, whereinthe control circuit includes at least one electrical energy accumulator.5. The device of claim 1, wherein the tool is a well bore drilling tooland the piezoelectric means comprises at least one assembly ofpiezoelectric elements housed into a main tubular body having a firstend connected to a stationary coupling device and a second end connectedto a movable coupling device capable of axially moving in the maintubular body for applying varying pressure onto the at least onepiezoelectric elements assembly, the at least one assembly ofpiezoelectric elements being connected to a control circuit foradjusting and/or regulating electrical parameters of the electricalenergy.
 6. The device of claim 5, wherein the at least one assembly ofpiezoelectric elements comprises at least one an array of piezoelectricdiscs that are axially arranged and connected to a stress restrictingdevice for preventing the array of discs from being affected byexcessive stresses and impacts.
 7. The device of claim 6, wherein the atleast one array of piezoelectric discs includes a first end and a secondend, the first end having two electrical connecting terminals and atleast one mechanical coupling bore, and the second end having twoelectrical connecting terminals and at least one mechanical couplingpin, with a first terminal of the first end being electrically connectedto a first terminal of the second end and a second terminal of the firstend being electrically connected to a second terminal of the second end.8. The device of claim 7, wherein the at least one array ofpiezoelectric discs comprises at least two axially connected arrays. 9.The device of claim 7, wherein the array of piezoelectric discs isaxially connected to an electrical adapting device forming part of thecontrol circuit, the adapting device including at least one transformerand a diode bridge.
 10. The device of claim 6, wherein the array ofpiezoelectric discs receives pressure vibrations along an axis accordingto piezo coefficient g33 of the piezoelectric discs.
 11. The device ofclaim 6, wherein the array of piezoelectric discs receives pressurevibrations along two normal axes according to piezo coefficients g33 andg31 of the piezoelectric discs.
 12. The device of claim 9, wherein thestationary coupling device comprises an electric concentring device thathouses a further part of the control circuit and at least one operationequipment.
 13. The device of claim 12, wherein the stationary couplingdevice, the electric concentring device, the movable coupling device andthe main body include axially extending orifices for passing drillingmud employed in the drilling of the well bore.
 14. The device of claim8, wherein the array of piezoelectric discs comprises an outer casinghousing at least two piezoelectric discs arranged axially side by side,facing to each other by their disc faces, and mounted on an electricallyinsulating shaft, the discs being electrically in-parallel connected tothe electrical connecting terminals.
 15. The device of claim 14, whereinthe electrically insulating shaft has an end including an adjustingscrew for compressing the array of piezoelectric discs.
 16. The deviceof claim 5, wherein the main tubular body has at least one notcharranged at the second end of the main tubular body, the movablecoupling device at least partially and axially moving within the maintubular body and including a key radially outwardly extending throughthe at least one notch for restricting the axial relative movementbetween the main tubular body and the movable coupling device.
 17. Thedevice of claim 12, wherein said part of the control circuit housed inthe concentring device comprises at least one capacitor and a tensionregulator.
 18. The device of claim 17, wherein the adapting device is adevice for adapting the tension and impedance of the electrical energyand is connected said further part of the control circuit.
 19. Thedevice of claim 6, wherein the stress restricting device is selectedfrom the group consisting of springs, high impact resisting rubber,Belleville-type discs springs, hydraulic springs.
 20. The device ofclaim 19, wherein the stress restricting device has a stiffness that maybe adjusted to reach the mechanical resonance of the electrical energygenerating device.
 21. The device of claim 1, wherein the piezoelectricmeans are made of a material selected from the group consisting ofceramics, crystals, composite materials, lead titanate, lead zirconate.22. The device of claim 5, further comprising accumulator means foraccumulating at least part of the electrical energy generated by thedevice.